I think it only broke for last targets that are not mobiles. If you use cycle cursor target last action to cycle thru mobiles, hitting the cursor target last action still works. If you spell target a mobile using current target, you can still use cursor target last to hit that same target with subsequent spells.
When I have a non-mobile as a spell target, cursor target last is broken as you state. Main impact for me is I can't use it to cast multiple nature furies on the ground using cursor target last.